In order to make an appropriate diagnosis of cardiac functions of a patient, display continuity for the cardiogram waveforms is required for a device that displays the cardiogram waveforms. For example, such continuity can not be maintained when the base-line of the cardiogram varies greatly by noises such as body movement of an examinee. There exists technology for maintaining display continuity of cardiogram waveforms of a cardiograph (see Patent document 1, for example). A technology by which saturation of the output from an amplifier for amplifying cardiogram signals being measured (or the input to an A/D converter) is avoided when the base-line of the cardiogram varies greatly by noises such as body movement (as disclosed in Patent document 1). Specifically, if the output of the amplifier exceeds a predetermined value, the waveform signals are made within a conversion range of the A/D converter in a short period of time by temporarily increasing a cut-off frequency of a low cut filter of a CR circuit in a cardiograph.    Patent document 1: Japanese laid-open publication No. Hei8-24670 (FIG. 1)